Communication 
  11.1 Communication via Modbus 
SIWAREX WT241 
Manual, 05/2015, A5E36046748Aa  95 
11.1.4  Command mailboxes 
Corresponding command codes must be sent in order to execute commands and to read 
and write data records in the Modbus buffer memories. These are described in more detail in 
chapter → Command lists (Page 87). The following tables list the Modbus registers used to 
process these commands: 
Table 11- 1  Command mailbox 1: Highest priority 
Code of command to be executed 
Trigger for starting the command 
0=job running; 1=job finished (1 cycle) 
0=no error; <>0=error code 
 
Table 11- 2  Command mailbox 2: Average priority 
Code of command to be executed 
Trigger for starting the command 
0=job running; 1=job finished (1 cycle) 
0=no error; <>0=error code 
 
Table 11- 3  Command mailbox 3: Low priority 
Code of command to be executed 
Trigger for starting the command 
0=job running; 1=job finished (1 cycle) 
0=no error; <>0=error code 
11.1.5  Reading registers 
The method for reading registers depends on whether they belong to the writable data 
records (DR 3 to DR 29) or can only be read as current values (DR 30 to DR 34). 
If you wish to read the registers from the data records DR 3 to DR 29, you must first export 
these as a complete data record to the internal output buffer.  
All Modbus registers of the individual parameters can be found in chapter → Scale 
parameters and functions of the belt scale (Page 59).